1. Field of the Invention
This invention relates to a plasma-generating device including a diamond layer having a graphite phase and/or a graphite precipitate layer.
2. Description of the Related Art
Diamond and its related materials are used in many technical fields due to their specific physical and chemical characteristics. Besides, because a diamond film has excellent electron field emission (EFE) property, it is beneficial to serve as a material for forming field emission emitters. In recent decades, many efforts have been devoted to study the growth, characteristics and applications of single-crystalline and microcrystalline diamond (MCD).
A method for fabricating a diamond film has been proposed by the inventors of this application (see “Growth behavior of nanocrystalline diamond films on ultra nanocrystalline diamond nuclei: The transmission electron microscopy studies,” Journal of Applied Physics 105, 124311 (2009)). The method includes: (A) disposing an n-type silicon substrate in a microwave plasma enhanced chemical vapor deposition (MPECVD) system under Ar/CH4 plasma condition, in which the volume percentage of CH4 is 1%, and performing a MPECVD process for 20 minutes so as to form a seed layer having a plurality of ultra-nanocrystalline diamond (UNCD) grains on the silicon substrate; and (B) disposing the silicon substrate having the seed layer in another MPECVD system (2.45 GHz, AS-TeX 5400) and performing a MPECVD process under a working pressure of 73 mbars in a mixed gas atmosphere (CH4/H4), in which the volume percentage of CH4 is 1%, for 60 minutes, so as to obtain a diamond film having a plurality of MCD grains.
The MCD grains of the diamond film have an average size of about 300 nm when observed using Scanning Electron Microscopy (SEM). When observed using Transmission Electron Microscopy (TEM), it is found that each of the MCD grains is surrounded by a plurality of UNCD grains having an average size near 10 nm. After analyzing field emission properties of the diamond film, the turn-on field (E0) is about 11.1 V/μm.
The turn-on field (E0) of the aforesaid diamond film is relatively high and further improvement is needed so as to meet requirements for field emission emitters.
U.S. Pat. No. 6,867,548 discloses a plasma-generating device that includes a cathode, an anode, a dielectric layer which is formed between the cathode and the anode, and a cavity which extends through the cathode and the dielectric layer. The cathode and the anode are configured to generate plasma in the cavity when a pulsed voltage is applied across the cathode and the anode. The cathode may be made of copper, aluminum, gold, silver, nickel, zinc, or a conductive polymer blended with carbon black.
Taiwan patent no. I313476 discloses a micro plasma-generating device that includes a cathode, an anode, and a micro tip formed on the cathode for tip discharging for generating plasma when a pulsed voltage is applied across the cathode and the anode. The cathode may be made of chromium.
However, metal or metal alloy, such as copper, has a low electron field emission (EFE) and/or a low hardness, which renders the same unsuitable to be used as the cathode material for the micro plasma-generating device.